Single-crystal growth and structure determination of misfit layer oxide [Sr2TlO3][CoO2]1.77

We have synthesized single crystals of the misfit layer cobaltate [Sr2TlO3][CoO2]1.77 and determined its crystal structure by the means of X-ray single-crystal diffraction (XRSD) and transmission electron microscopy. The synthesis took place by spontaneous crystallization from an oxide melt at high gaseous pressure. The structure is described by two monoclinic subsystems, which share the unit cell parameters, a=4.933(5) Å, c=11.470(12) Å, and β=98.00(10)°, but are incommensurate in the direction of b-axes: b1=5.009(8) Å and b2=2.830(8) Å, where b1 is for the subsystem [Sr2TlO3] and b2 for [CoO2]. The layer sequence in the structure consists of CdI2-type structured (CoO2)∞ and three puckered rock-salt (RS) layers, two of which are (SrO)∞ and one (TlO)∞. The solved structure confirms that the thermoelectric compounds [Ca2CoO3][CoO2]1.62 (Co-121) and [Sr2TlO3][CoO2]1.77 (Tl-121) are isostructural.